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<title>realloc</title>
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<h2 align=center>realloc</h2>
<h4 align=center>OS/161 Reference Manual</h4>

<h3>Name</h3>
<p>
realloc - resize allocated memory
</p>

<h3>Library</h3>
<p>
Standard C Library (libc, -lc)
</p>

<h3>Synopsis</h3>
<p>
<tt>#include &lt;stdlib.h&gt;</tt><br>
<br>
<tt>void *</tt><br>
<tt>realloc(void *</tt><em>ptr</em><tt>,
size_t </tt><em>newsize</em><tt>);</tt>
</p>

<h3>Description</h3>
<p>
<tt>realloc</tt> attempts to change the size of the memory block
pointed to by <em>ptr</em> to <em>newsize</em>, causing the block to
shrink or grow as necessary. If the size cannot be changed, a new
block is allocated and the contents (up to the lesser of the previous
size and <em>newsize</em>) are copied, then the old block is freed.
</p>

<p>
The size of <tt>NULL</tt> is treated as 0. If the size is increased,
any newly allocated space has undefined contents. If the size is
decreased, the space discarded may no longer be accessed. Otherwise
the contents of the memory block are preserved.
</p>

<p>
<em>ptr</em> must be NULL or have been previously returned by
<A HREF=malloc.html>malloc</A>, <A HREF=calloc.html>calloc</A>, or
realloc.
</p>

The alignment and other restrictions described for
<A HREF=malloc.html>malloc</A> apply equally to realloc.
<p>

<h3>Return Values</h3>
<p>
<tt>realloc</tt> returns a pointer to the resized memory block. This
may not be the same pointer as <em>ptr</em>. If so, the old block is
invalidated and <em>ptr</em> becomes invalid.
</p>

<p>
If the operation cannot be performed at all, NULL is returned and
the original block pointed to by <em>ptr</em> is untouched
and remains valid.
</p>

<h3>See Also</h3>
<p>
<A HREF=calloc.html>calloc</A>,
<A HREF=malloc.html>malloc</A>,
<A HREF=free.html>free</A>
</p>

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